1. Technical Field of the Invention
The present invention relates to polymer particles which are especially suitable as toner particles for electrophotographic processes, to electrophotographic processes for production of three-dimensional structures on a support structure, and to the three-dimensional structures produced by means of these processes.
2. Related Art
The manufacture of three-dimensional objects with the aid of computer-generated models is constantly gaining significance. This involves regular buildup layer by layer, which enables individual matching of the desired structure. The demand for components formed from several component parts and the increasingly complex geometry thereof increases the requirements with regard to the spatial resolution of the manufacturing process. Particularly in medical technology, the specific manufacture of transplants is associated with great complexity, since the objects have to be matched individually to each patient.
There are various known processes which enable the buildup of three-dimensional objects from plastic. They are encompassed by the name “Rapid Prototyping” (or “solid freeform fabrication”) (Wang, Trends in Biotechnology, 25 (11), pages 505 to 513). However, these processes are either restricted to the application of a single polymer component or have resolutions above >250 μm.
The fusion of toner or polymer particles by means of electromagnetic radiation is known by the name “non-contact fusing”. In this process, the electromagnetic radiation is used as a heat source for the fusion of the polymer. Chemical fixing of the toner particles to one another is not achieved (JP 002000035689, JP 002004177660, US 000004435069 A, DE 000010064563 A1).
Electrophotography (“laser printing”) has proved in the last few decades to be a reliable method for two-dimensional text printing with comparatively high resolution (1200 dpi, resolution <50 μm). Accordingly, electrophotography constitutes a widespread printing technique with which technical surfaces, usually in the form of paper or film surfaces, can be printed with substances in powder form. In principle, electrophotography involves electrostatic charging, for example with the aid of a preliminary charging roller or a corona, of a rotating photographic roller coated with a photosemiconductor material, followed by exposure at local sites by means of a laser arrangement or an LED array, as a result of which it is at least partly electrically discharged at these exposed regions. All other unexposed regions of the photographic roller remain electrically charged and correspond to the negative image of the two-dimensional structures to be printed, for example in the form of text, images etc. In a subsequent step, pulverulent toner is applied to the exposed photographic roller, the toner being electrostatically charged by friction in the printer and therefore being able to adhere only to the discharged regions of the photographic roller. To influence the electrostatic charging of the toner, modern commercially available toners contain about 2 to 4% by volume of charge control additives. The predominant constituent of the toner, i.e. about 80 to 90% by volume, consists typically of a dry solvent, called the matrix, which typically consists of a mixture of synthetic resin and wax. In a proportion of about 5 to 18% by volume, the toner contains a dye component, for example in the form of carbon black.
There are also known electrophotographic processes with which multilayer objects made from metal powder can be printed (van der Eijk et al., Metal Printing Process: A Rapid Manufacturing Process Based on Xerography using Metal Powders Materials, Science & Technology, 2005). In addition, electrophotographic obtained surfaces have been three-dimensionally structured with the aid of foaming agents (JP 002005004142 AA). However, the resolution cannot be controlled adequately and is restricted to the toner layer present on the support structure. This method therefore does not offer the possibility of generating a three-dimensional object layer by layer.
There are likewise known electrophotographic processes in which the adhesion of the toner on the support structure is increased with the aid of curing reactive groups (U.S. Pat. No. 5,888,689) and/or by post-crosslinking the particles through the addition of photoinitiators (WO 2006/027264 A1, EP 0 667 381 B1, EP 0 952 498 A1). There is also a known process for production of toner materials comprising UV-polymerizable additives (US 000005212526 A). However, these processes achieve solely improved adhesion on the support structure surface and do not ensure the controlled three-dimensional buildup of polymer layers.
However, the use of such processes for biologically and medically usable three-dimensional plastic parts is a problem which has not been solved to date, particularly owing to the need for three-dimensional fixing of the individual particles (U.S. Pat. No. 6,066,285 A).
The technical problem underlying the present invention is to provide processes and means which overcome the aforementioned disadvantages, more particularly processes and means which allow production of high-resolution three-dimensional structures, especially in the μm and/or mm range, especially in a rapidly performable and inexpensive process, and wherein the products produced may also be biocompatible and biofunctional. More particularly, the present invention is based on the technical problem of providing high-resolution three-dimensional structures of the aforementioned type, which can be used, for example, as transplants, in tissue engineering processes or products, as tube structures or the like.